I'll add a few things. First, I started using an ultrasonic machine to clean records when the Audio Desk original model came out. I found that it did a nice job on well preserved and new records but if you buy older copies, or have copies with a questionable cleaning history, you need to use a manual cleaning method (combined with vacuum) to clean some deeply contaminated records effectively-- that ultrasonic alone won't do it despite the convenience, lack of physical contact with the groove surface, etc.
I also found that a lot of the problems with "used" records probably resulted from previous "bad" cleanings- sprays, wipes, etc. This form of contamination is essentially the residue of cleaning agents that were not effectively removed from the record.
Third, and think Neil addresses this, the number of records in a given bath, spacing, location of transducers and the ultrasonic machine's power in relation to the bath size all factor in to effectiveness of the ultrasonic process; there is some science to this and its also understandable when you consider how cavitation works: waves creating imploding bubbles. The implosions are what cleans.
A machine that does ten records at a time is not necessarily going to clean more effectively than one that only does a single or double LP at a time; it could be less effective, though it sounds more convenient. This can all be calculated.
You also have to consider whether you are going to use chemistry; it will enhance the cavitation effect by reducing the surface tension of the bath water, but you also have to remove the chemical residue once done. This takes us full circle to my comment about past bad cleanings.
I'm sure Neil (@antinn) can correct anything I mistook above; I don't have the science or engineering chops but arrived at a lot of these conclusions through experimentation. And, I'm happy to say that I published Neil's book, Precision Aqueous Cleaning of Vinyl Records, and in the course of doing so, learned a hell of a lot about why certain things work and others are less effective or cause problems.
